GENERATION OF MAXWELL DISPLACEMENT CURRENT ACROSS AN AZOBENZENE MONOLAYER BY PHOTOISOMERIZATION

INTEREST in the behaviour of Langmuir-Blodgett (LB) films 1 is motivated by possible applications that include molecular electronics, biosensors and modelling of biological membranes. We recently 2-5 reported an electrical technique that allows molecular motions in LB films to be probed by measuring the Maxwell displacement current 6 generated across electrodes above and below the film: this current results from changes in the orientation of the molecular dipoles. Here we use the technique to study the effect of photoisomerization in an LB film consisting of an azobenzene derivative, which can be switched photochemically between cis and trans isomers. Films of this sort are of particular interest because of their possible use in information-storage devices 7-11. Successive isomerizations induced by irradiation with ultraviolet and visible light produced transient displacement-current pulses between the electrodes. We anticipate that this technique will become widely used for dynamical studies of LB films.